Fresh Water
noun, の adjective
A faint water is water that's not thick with salt. It's fresh water.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
金魚は淡水魚だから、水槽に塩を入れてはいけませんよ。
Goldfish are freshwater fish so you shouldn’t put salt in the tank.